I haven't been there since back in the 90s, so I don't know what may have changed since then. It was built as a cross-country ski trail (a very nice one at that). Lots of hills, but built for skiing so no single track, no tight switchbacks, nothing really technical. You can hike up to the top of Pincushion Mtn from the far end of the big loop (I took my bike up their back in the day, but I'm thinking they probably don't allow that).

Any Update?

I'm going up to Lutsen in late October and apparently the resort doesn't have any more MB trails. As they so eloquently put it:

Due to growing concerns regarding liability issues and our environmental objectives related to the Poplar River, Lutsen Mountains regrets to inform our guests that we will no longer be offering mountain biking as part of our summer activities roster.

Pincushion is great! I checked it out the end of August.
It is 5-6 Miles long now, I talked to a guy working on it and he said they are working on making it 25Miles long. (The picture is from the top of Pincushion) Amazing view
Also just south of Lutsen in Tofte go up the Sawbill Trail about 3 miles.
When the pavement ends and turns to dirt road there is a parking lot on the right-hand side. There are great single track trails. The trail map is on the bulletin board in the lot.

Don't know if you've ridden there yet this summer but we have a lot of new trail that opened this year. We have completed the access trail from the parking lot so you can now ride totally on single track from the parking lot and do the loop completed last season, the old back 80 loop and by the end of Oct. the new lower loop will be completed as well.